Exploring, drilling and completing hydrocarbon and other wells are generally complicated, time consuming and ultimately very expensive endeavors. In recognition of these expenses, added emphasis has been placed on efficiencies associated with well completions and maintenance over the life of the well. Over the years, ever increasing well depths and sophisticated architecture have made reductions in time and effort spent in completions and maintenance operations of even greater focus.
In terms of architecture, the terminal end of a cased well often extends into an open-hole section. Thus, completions hardware may be fairly complex and of uniquely configured parts, depending on the particular location and function to be served. For example, in addition to the noted casing, the hardware may include gravel packing, sleeves, screens and other equipment particularly suited for installation in the open-hole section at the end of the well. However, hardware supporting zonal or formation isolation may be located above the open-hole section. Further, certain features such as chemical injection lines may traverse both cased and open-hole well regions. Once more, such complex architecture may need to remain flexible enough in terms of design and installation sequence so as to account for perforating, fracturing, gravel packing and a host of other applications that may be employed in completing the well.
With the above factors in mind, the sequence of hardware installation, following drilling and casing of the well, may begin with gravel packing directed at the open-hole productive region of the well. In terms of hardware delivery for a corresponding lower completion, this may include the installation of screen equipment, a gravel pack packer, a frac sleeve and other features at this productive interface. The result is a cased well that now terminates at a lower completion having at least a temporary degree of fluid control with frac sleeves closed over the formation interface at the lower completion. Further, subsequently, or in conjunction with, the lower completion installation, a more secure mechanical formation isolation valve (MFIV) may be installed. Thus, a more reliable and permanent form of control may be provided.
Generally, once the MFIV is installed, it is also simultaneously closed as the installation tools are removed from the well. For example, a shifting tool at the end of a workstring may close the valve automatically as the workstring is removed. Thus, the upper completion may be subsequently installed over, and in communication with the MFIV as overall completions are finished out.
In many cases, the upper and lower completions are connected together at the location of the MFIV, perhaps through an intermediate completion, and with hydraulic control through each completion segment so as to maintain control over the MFIV. For example, wet-mate hydraulic connections may be utilized to couple hydraulic lines of the various completions segments and to the MFIV. In this manner, control over opening and closing of the valve from surface may be provided. Thus, when the upper completion is fully landed and secured, the MFIV may be opened via hydraulic control from surface.
Unfortunately, seals in downhole hardware will degrade over time and may start leaking. This may require a major work over of the completion which is very expensive. Also sealed connections between lines through a wet-mating hydraulics may not be as reliable, for example in the presence of natural debris in the downhole environment. So, for example, while the life of the well may be upwards of twenty years, seals are unlikely to remain reliable for as many as ten years. Thus, control over the MFIV is likely lost at some point with opening and closing thereafter, requiring a more costly and time consuming dedicated intervention. For example, well operations may be brought to a halt and a shifting tool at the end of a coiled tubing or other suitable conveyance may be run into the well to open and close the MFIV as needed. Such interventions are not only costly, they are not always practical. That is, in many cases, an electric submersible pump (ESP) or other later installed production hardware may have been located within the wellbore and act as an impediment to accessing the MFIV through such an intervention. As a result, a degree of equipment removal and follow-on workover may be required just to be able to open or close the MFIV a single time.
Efforts have been undertaken to exercise control over the MFIV without reliance on wet-mate hydraulics or follow on dedicated intervention. This is particularly the case for wells that are configured to employ ESP-type equipment within the wellbore at the onset of well operations. For example, the upper completion may be outfitted with a shifting tool at the end thereof. Thus, the MFIV may be initially opened in conjunction with the installation of the upper completion. As a result, communication throughout the wellbore, between completion segments, is attained as soon as the upper completion is installed.
Unfortunately, utilizing a shifting tool that extends from below the upper completion segment to automatically open the MFIV means that the MFIV will open before the upper completion is fully landed out and sealably installed. Thus, where a significant pressure differential is present in the bore of the isolated lower completion, well control may be lost for a period of time as the upper completion is installed. An attempt may be made to quickly raise the upper completion and close the valve. However, where pressure is high enough this could translate into a blowout of catastrophic proportions nonetheless. As a result, where such lower wellbore pressures are considered likely, operators are left with the only practical option of wet-mate hydraulics and dedicated interventions, irrespective of the limited life and overall expenses which may be involved.